Sanitary articles such as sanitary napkins, baby diapers, absorbent inserts, and absorbent adult incontinence articles are well-known in the art. Typically all these articles comprise a wearer facing surface and a garment facing surface. The wearer facing surface receives from the wearer of such articles liquids, bodily discharges such as urins, vaginal discharges or menses, to be absorbed. In order for the article to store the liquid the wearer facing surface has to be liquid permeable while maintaining integrity of the outer wearer facing surface of the absorbent article. This wearer facing surface is provided by a topsheet.
Well-known topsheets in the art of absorbent articles are non-woven fabrics, woven fabrics or films. Films have to be rendered permeable by aperturing. Fabrics or non-woven fabrics are made of fibers which by their nature provide non-linear apertures in the liquid transport direction. Also the largest aperture size in fabric topsheets is limited by the requirement to maintain material strength.
Films are often made of polymeric material and typically comprise apertures which have been engineered to provide certain characteristics. These apertures can vary in shape and size but have commonly been provided in a single preferred size and shape. The walls of the apertures define the amount of extension-if any- beyond the plane of the film thickness and the direction of such extensions. The film apertures also can be provided in the shape of a funnel. Films are generally preferred over fabrics since they can provide a cleaner surface even after liquid having passed through since they do not retain liquids.
A typical topsheet made of polyethylene film has been successfully used in sanitary articles and adult incontinence products as well as inserts and baby diapers. One problem remaining is the rate of liquid capable of passing through such a topsheet under usual usage conditions due to the total amount of open area of all apertures and individual aperture size and shape in particular. Exceptionally large apertures increase the liquid passage rate but pose the potential problem of material stability for the topsheet film at least during the manufacturing of absorbent articles, which is highly undesirable. Also large apertures possibly promote a backflow of absorbed liquid, so called rewet, which is undesirable. Small individual apertures on the other hand cannot provide the liquid passage characteristics required to let liquids of high surface tension, high viscosity or solid content such as coagulated blood clots pass through; this can be a problem in an absolute sense for very small apertures or cause too low a rate of liquid flow.
It also has been found that the total amount of open area for a given aperture size and shape is approximately linearly related to the rate of liquid passage. Again, masking of the liquid which has passed through but also material strength and other appearance considerations are limiting the extend as to which the total open area in a film topsheet can be selected.
It is also known that the viscosity of liquids disposed on sanitary napkins can very drastically from exceptionally low viscosities e.g. of urine from a person having a light incontinence or stress incontinence syndrome. Low viscosities also can be present for vaginal discharges or menses which comprise small amounts of surfactant. Some bodily discharges comprise natural surfactants already but also residue from washing soaps, which many wearers of such articles use regularly, can be found.
At the other end of the spectrum viscosities of menses changes drastically over the period of a woman and have been reported in EP-A-0 205 286 to range from 5 to 50 mPas. The viscosities can change over time on the same person and can vary between persons compared at a similar stage of the monthly period.
It is therefore an objective of the present invention to provide a film topsheet for sanitary articles which can accommodate the viscosity changes without the need for different articles for different times. It has been found that this can be achieved by providing topsheets for absorbent disposable articles which have apertures of different open areas. These open areas should correspond to a range of the viscosity distribution of the liquids expected to be absorbed.
It is hence an objective of the present invention to provide absorbent articles which have a film topsheet with a distribution of aperture sizes.